Electron amplifier utilizing carbon nanotubes and method of manufacturing the same

ABSTRACT

An electron amplifier and a method of manufacturing the same are provided. The electron amplifier includes a substrate in which a plurality of through holes are formed, a resistive layer deposited on the sidewalls of the through holes, an electron emissive layer including carbon nanotubes which is deposited on the resistive layer, and an electrode layer formed on each of the upper and lower sides of the substrate. Because the electron emissive layer of the electron amplifier is uniform and provides a high electron emission efficiency, the electron amplification efficiency is improved. The electron amplifier manufacturing method enables economical mass production of electron amplifiers.

BACKGROUND OF THE INVENTION

[0001] This application claims priority from Korean Patent ApplicationNo. 2002-9088, filed on Feb. 20, 2002, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to an electron amplifier and amethod of manufacturing the same, and more particularly, to an electronamplifier utilizing carbon nanotubes and a method of manufacturing theelectron amplifier.

[0004] 2. Description of the Related Art

[0005] Electron amplifiers include a secondary electron emission layerin order to induce emission of secondary electrons. Electron amplifiersare based on the principle that if primary electrons are accelerated tocollide with the secondary electron emission layer, bound electrons onthe surface of the secondary electron emission layer absorb the kineticenergy of the primary electrons, and are then emitted as secondaryelectrons.

[0006] Electron amplifiers are generally used in measuring equipment,such as, mass analyzers, surface analyzers, energy analyzers, and thelike, and are also used in night goggles, display devices, and the like.

[0007]FIG. 1A is a cross-section of a conventional electron amplifier10. Referring to FIG. 1A, the conventional electron amplifier 10includes a substrate 13, electrode layers 14 and 15 formed on the upperand lower surfaces of the substrate 13, respectively, a through hole 11formed perpendicular to the electron layers 14 and 15, a resistive layer16 formed along the inner wall of the through hole 11, and an electronemission layer 17 formed covering the resistive layer 16.

[0008]FIG. 1B illustrates a method of manufacturing a conventionalelectron amplifier. As shown in step (a), a core glass 22 which melts ina chemical etching solution and a lead glass 21 which does not melt inthe chemical etching solution are prepared. As shown in step (b), thecore glass 22 fits into the lead glass 21 to obtain a single glass pipe23. Thereafter, the single glass pipe 23 is stretched to obtain a thinglass fiber 23′ as shown in step (c). Then, glass fibers 23 are tiedinto a hexagonal bundle 24 as shown in step (d). Next, the hexagonalbundle is stretched out to obtain a thin hexagonal multiple fiber 25 asshown in step (e). Next, hexagonal multiple fibers 25 are tied into abundle 26, and the bundle 26 is then attached to a glass skin to beshaped as shown in step (f). The bundle 26 is then thinly cut to obtaina wafer 27 as shown in step (g).

[0009] Next, the surface of the wafer 27 is polished, and the core glass22 of the glass fiber 23′ is etched using an appropriate etchingsolution. Then, the resultant wafer 27 undergoes a chemical process forincreasing the secondary electron emission property of the wall of theglass fiber 23 and is then reduced in a hydrogen-ambient baking furnace.During this reduction, lead oxide on the glass surface turns intoconductive lead and water, and lead particles form lumps. If thetemperature is high, lead particle lumping prevails over new leadparticle formation. Thus, the resistance between two electrodes is notdetermined by lead particles but by the temperature in the bakingfurnace.

[0010] Finally, an electrode is formed of Inconel or Nichrome on thebaked wafer 27, thereby completing a microchannel plate.

[0011] The electrical operation characteristics of electron amplifiersare usually determined by their resistance, which in turn is determinedby the ratio of the length of a through hole to the diameter thereof.Accordingly, it is difficult for conventional electron amplifiers toobtain a desired electron emission efficiency, for example, an electronemission efficiency of 10³ through 10⁵ times as much as a primaryelectron emission efficiency.

SUMMARY OF THE INVENTION

[0012] The present invention provides an electron amplifier with anexcellent secondary electron emission property, and a method of simplymanufacturing an electron amplifier, by which large display devicescreens can be easily manufactured.

[0013] According to an aspect of the present invention, there isprovided an electron amplifier including a substrate in which aplurality of through holes are formed, a resistive layer deposited onthe sidewalls of the through holes, an electron emissive layer depositedon the resistive layer and including carbon nanotubes, and an electrodelayer formed on each of the upper and lower sides of the substrate.

[0014] According to another aspect of the present invention, there isprovided a method of manufacturing an electron amplifier. In the method,first, through holes are formed in a substrate. Next, a resistive layeris formed on the sidewalls of the through holes. Thereafter, carbonnanotubes are added to a sol-gel solution of a material with a highsecondary electron emission coefficient. Then, an electron emissivelayer is deposited on the resistive layer by dipping the substratehaving the through holes and the resistive layer into the sol-gelsolution. Then, the substrate on which the through holes, the resistivelayer, and the electron emission layer are formed is baked. An electrodelayer is then formed on each of the upper and lower sides of thesubstrate so as to be perpendicular to the through holes.

[0015] Preferably, the electron emissive layer is formed of any ofoxide-based and fluoride-based materials having a high secondaryelectron emission coefficient.

[0016] It is also preferable that the oxide-based material is one ofMgO, SiO₂, and La₂O₃, and the fluoride-based material is one of CaF₂ andMgF₂.

[0017] Preferably, the substrate is formed of any material selected fromthe group consisting of any glass, any ceramic, Al₂O₃, Cu, and Si.

[0018] In the electron amplifier according to the present invention, asecondary electron emission film is formed by mixing carbon nanotubeswith a material having a high secondary electron emission efficiency.Thus, the electron amplifier provides a high secondary electron emissionefficiency. Also, because the electron amplifier is simply manufacturedusing a sol-gel method, large display device screens can be economicallymass-produced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other features and advantages of the presentinvention will become more apparent by describing in detail exemplaryembodiments thereof with reference to the attached drawings in which:

[0020]FIG. 1A is a cross-section of a conventional electron amplifier;

[0021]FIG. 1B illustrates a method of manufacturing a conventionalelectron amplifier;

[0022]FIG. 2 is a perspective view of an electron amplifier according toan embodiment of the present invention;

[0023]FIG. 3A is a plan view of an electron amplifier according to anembodiment of the present invention;

[0024]FIG. 3B is a magnified view of circle A of FIG. 3A;

[0025]FIG. 3C is a magnified view of circle B of FIG. 3B;

[0026]FIGS. 4A through 4E illustrate steps before an electron emissionfilm deposition step in a method of manufacturing an electron amplifieraccording to an embodiment of the present invention;

[0027]FIG. 5 illustrates the electron emission film deposition step inthe method of manufacturing the electron amplifier according to anembodiment of the present invention; and

[0028]FIG. 6 is a graph of secondary electron emission efficiency (δ)versus net energy of primary electrons of a secondary electron emissionfilm installed in an electron amplifier according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will now be described more fully withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. Throughout the drawings, the same referencenumerals denote the same members.

[0030] Referring to FIG. 2, an electron amplifier according to anembodiment of the present invention includes a substrate 33, a pluralityof through holes 32 formed in the substrate 33, a resistive layer 35formed along the inner wall of each of the through holes 32, an electronemission layer 37 deposited on the resistive layer 35 and includingcarbon nanotubes 45, and upper and lower electrode layers 31 formed onthe upper and lower sides of the substrate 33, respectively, so as to beperpendicular to the through holes 32.

[0031] The substrate 33 is formed of glass, ceramic such as Al₂O₃, ormetal such as Cu or Si.

[0032] The resistive layer 35 is formed of metal oxide with sufficientresistance to prevent an electrical short-circuit of the upper and lowerelectrode layers 31, and allow electrons to be adequately supplied tothe electron emission layer 37 against voltage received from a powersource.

[0033] The electron emission layer 37 is formed of the carbon nanotubes45 together with an oxide-based or fluoride-based material having highsecondary electron emission efficiency. A secondary electron emissioncoefficient denotes a ratio of the number of incident primary electronsto the number of emitted secondary electrons.

[0034] The carbon nanotube 45, a nano-sized graphite surface rolled intoa cylindrical shape, is known to have unique physical propertiesdepending on its shape and size. Frank reported in 1998 that, accordingto a scanning probing microscopy (SPM) measurement of the conductivityof a carbon nano fiber dipped in a liquid, carbon nanotubes exhibitquantum behaviour and have remarkably high conductivity. Carbonnanotubes have been observed to provide a stable current density of10⁷A/cm² or greater by Frank et al. and a stable current density of10¹³A/cm² or greater by Avoris et al.

[0035] Because of the excellent electrical characteristics of carbonnanotubes, the manufacture of display devices, electron guns, lithiumbatteries, and transistors, using the electron emission property ofcarbon nanotubes, has been actively studied of late.

[0036] The carbon nanotubes 45 used in an electron amplifier accordingto the present invention can be manufactured using an arc dischargemethod, a laser vaporization method, a plasma enhanced chemical vapordeposition (PECVD) method, a thermal chemical vapor deposition (TCVD)method, or a vapor phase growth method.

[0037] Among materials with a high secondary electron emissioncoefficient to form the electron emission layer 35, examples of anoxide-like material include MgO, SiO₂, and La₂O₃, and examples of afluoride-like material include MgF₂ and CaF₂.

[0038] The electron of atoms making up the surface of the electronemission layer 35 absorbs the kinetic energy of a primary electron,which is emitted from an external source, when the primary electroncollides with the surface of the electron emission layer 35, and is thenemitted from the surface of the electron emission layer 35 against aCoulomb attraction. Because the electron is emitted by the kineticenergy of the primary electron, the emitted outermost electron is calleda secondary electron. As the secondary electron emission coefficient ofthe electron emission layer 35 increases, more secondary electrons areemitted. The number of secondary electrons emitted can be calculatedfrom measured current because current depends on a consecutive flow ofsecondary electrons.

[0039]FIGS. 3A through 3C are pictures of an electron amplifieraccording to an embodiment of the present invention. FIG. 3A shows thetop surface of the electron amplifier according to an embodiment of thepresent invention. FIG. 3B is a magnified picture of circle A of FIG.3A. FIG. 3C is a magnified picture of circle B of FIG. 3B. In FIG. 3C,reference numeral 33 denotes a substrate made of alumina Al₂O₃,reference numeral 35 denotes a resistive layer made of CuAl₂O₄, andreference numeral 37 denotes an electron emissive layer made of SiO₂ orMgO.

[0040]FIGS. 4A through 4E and 5 illustrate a method of manufacturing anelectron amplifier according to an embodiment of the present invention.First, as shown in FIG. 4A, a substrate 33 is formed of an alumina pasteand then dried. The dried alumina substrate 33 is soft enough to easilyform through holes 32 as shown in FIG. 4B.

[0041] Next, the substrate 33 with the through holes 32 is compressedinto a thin plate, and a plurality of thin substrates 33 are piled ontop of one another as shown in FIG. 4C. Thereafter, the piled substrates33 are baked to form a basic structure 30 of an electron amplifier asshown in FIG. 4D.

[0042] Then, Cu or Ni is deposited on the basic structure 30 usingelectron beams, a sputtering (deposition) method, or a plating method,and then baked. Accordingly, CuAl₂O₄, CuO, or NiAl₂O₄ flows along theinner walls of the through holes 32, thereby forming resistive layers 35as shown in FIG. 4E.

[0043]FIG. 5 illustrates a process of forming an electron emissive filmon the basic structure 30 completed through the steps of FIGS. 4Athrough 4E. Referring to FIG. 5, a sol-gel solution of materials with anexcellent secondary electron emission property, for example, a SiO₂ orMgO sol-gel solution 43, is stored in a vessel 41, and the carbonnanotubes 45 are dispersed in the sol-gel solution 43. The basicstructure 30 completed in FIG. 4E is dipped in the sol-gel solution 43and then baked for a short period of time at a low temperature.Accordingly, an electron emissive layer 37 including the carbonnanotubes 45 is formed along the surface of the resistive layer 35,thereby completing the fabrication of an electron amplifier 30 accordingto an embodiment of the present invention as shown in FIG. 2.

[0044]FIG. 6 is a graph showing the emission characteristics of asecondary electron emissive film including carbon nanotubes used in anelectron amplifier according to an embodiment of the present invention.Carbon nanotubes of 0.015 g were dispersed in a solution mixed with1,3-propanediol (C₃H₈O₂), MgO acetate (MG(CH₃CO₂)₂.4H₂O), and MgO toobtain an 0.65M MgO solution. Then, a secondary electron emissive filmwas coated on a silicon substrate using the above-describedmanufacturing method. The graph of FIG. 6 shows secondary electronemission efficiency (δ) versus the net energy of the primary electrons,that is, energy corresponding to the difference between a primaryelectron energy (Ep) and a bias potential. Here, the secondary electronemission efficiency (δ) represents how many secondary electrons areemitted when primary electrons collide with the silicon substrate onwhich the secondary electron emissive film is formed.

[0045] The secondary electron emission efficiency (δ) denotes a ratio ofsecondary electron current with respect to primary electron current. Asshown in FIG. 6, when the net energy is 300 (eV), the highest secondaryelectron emission efficiency (δ) is provided. Accordingly, the netenergy at which the secondary electron emission efficiency is thehighest, as in the above experiment, is used to provide a highlyefficient electron amplifier.

[0046] The electron amplifier according to an embodiment of the presentinvention can be simply manufactured at a low cost using themanufacturing method using a sol-gel solution. Also, a pure, uniformelectron emissive layer can be obtained at a low temperature. Thus, theelectron amplifier is suitable for large display device screens. Inparticular, because the electron emissive layer is formed by addingcarbon nanotubes to a material with an excellent secondary electronemission property, the electron emissive layer provides a significantlyhigher secondary electron emission efficiency than existing electronemissive layers.

[0047] Because of these improved electron emission characteristics, adesired secondary electron emission efficiency can be obtained withouthaving to increase the primary electron current or adjust the dimensionsof the through holes. Thus, a limit in the ratio of the length of athrough hole to the diameter thereof is overcome, which facilitates morecontrol over an electrical performance in the manufacture of an electronamplifier.

[0048] While the present invention has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present invention as defined by the following claims.For example, other materials with an excellent secondary electronemission efficiency, not mentioned herein, can be used to fabricate anelectron amplifier according to the present invention.

What is claimed is:
 1. An electron amplifier comprising: a substrate inwhich a plurality of through holes are formed; a resistive layerdeposited on the sidewalls of the through holes; an electron emissivelayer deposited on the resistive layer and including carbon nanotubes;and an electrode layer formed on each of the upper and lower sides ofthe substrate.
 2. The electron amplifier of claim 1, wherein theelectron emissive layer is formed of any of oxide-based andfluoride-based materials having a high secondary electron emissioncoefficient.
 3. The electron amplifier of claim 2, wherein theoxide-based material is one of MgO, SiO₂, and La₂O₃.
 4. The electronamplifier of claim 2, wherein the fluoride-based material is one of CaF₂and MgF₂.
 5. The electron amplifier of claim 1, wherein the substrate isformed of any material selected from the group consisting of any glass,any ceramic, Al₂O₃, Cu, and Si.
 6. A method of manufacturing an electronamplifier, the method comprising the steps of: (a) forming through holesin a substrate; (b) depositing a resistive layer on the sidewalls of thethrough holes; (c) adding carbon nanotubes to a sol-gel solution of amaterial with a high secondary electron emission coefficient; (d)depositing an electron emissive layer on the resistive layer by dippingthe substrate having the through holes and the resistive layer into thesol-gel solution; (e) baking the substrate on which the through holes,the resistive layer, and the electron emission layer are formed; and (f)forming an electrode layer on each of the upper and lower sides of thesubstrate so as to be perpendicular to the through holes.
 7. The methodof claim 6, wherein the electron emissive layer is formed of any ofoxide-based and fluoride-based materials having a high secondaryelectron emission coefficient.
 8. The method of claim 7, wherein theoxide-based material is one of MgO, SiO₂, and La₂O₃.
 9. The method ofclaim 7, wherein the fluoride-based material is one of CaF₂ and MgF₂.10. The method of claim 6, wherein the substrate is formed of anymaterial selected from the group consisting of any glass, any ceramic,Al₂O₃, Cu, and Si.